The earliest Synthetic Aperture Radar (SAR) systems collected data with the radar's antenna aimed broadside to the aircraft's flight path. Images formed from this data were displayed in a natural coordinate system with axes oriented in directions parallel to the flight path, and orthogonal to the flight path. These directions were typically respectively called “along-track” and “cross-track”, which emphasized their alignment with the aircraft's flight track.
Later, more sophisticated SAR systems collected data with the radar's antenna pointed in directions other than broadside to the aircraft. This geometry was termed “squint” operation. The image formation process then yielded a more natural image coordinate frame where principal axes were aligned with the bearing from aircraft to target scene, and orthogonal to this on the ground. These directions were often referred to as “range” and “cross-range”, which emphasized their alignment with target bearing.
To be sure, once an image is formed, it can be rotated to any other orientation using well-known image processing techniques. However, for arbitrary-angle rotations these algorithms are computationally expensive, involving multi-dimensional interpolation and resampling of the data. These operations also often cause the data to lose fidelity, and are particularly problematic for the complex images normally associated with SAR. Complex pixel information refers to each image element (pixel) having both a magnitude and phase component, or equivalent. Complex images are necessary for many subsequent image exploitation techniques such as Interferometric SAR (InSAR, IFSAR) and Coherent Change Detection (CCD).
It is therefore desirable to alleviate the aforementioned difficulties associated with conventional approaches to SAR image rotation. According to exemplary embodiments of the present invention, this can be addressed by adjusting the SAR data collection operation based on the desired rotation. The SAR data collected by the adjusted SAR data collection operation can then be efficiently exploited to form therefrom a SAR image having the desired rotational orientation.